It is generally recognized that the amount of organic material in the form of BOD (biological oxygen demand), COD (chemical oxygen demand), and color bodies currently being discharged into public water supplies from pulp and paper mills is a problem of increasing importance in water pollution.
In the manufacture of paper, cellulose from both hard woods and soft woods is converted to pulp by various processes such as the sulfite process and the sulfate process and the pulp is subjected to various treatments particularly bleaching which involve the use of chemical reagents such as chlorine, chlorine dioxide, sodium hypochlorite and caustic alkalis. As a result of these treatments, the paper making process produces highly colored effluents. The bleaching of the pulp, in particular the caustic extract effluent, is a major contributor to pollution problems.
Lignin is a primary source of color in the pulp. Chlorination of the pulp during the bleaching operation results in the formation of color bodies which are leached from the pulp by caustic alkali solutions. Thus, the caustic extract effluent contains a major proportion of the color bodies and other organic materials which have to be disposed of in waste water treatment.
Several processes are now used or advocated for use in removing color from paper mill waste. One of these is the so-called "massive lime process". This process utilizes lime in quantities ranging from 5,000 to 20,000 parts per million (ppm) to remove by coagulation and sedimentation techniques the organic colored bodies from paper mill wastes.
Another process which is disclosed in U.S. Pat. No. 3,412,018 involves the use of certain types of water insoluble amines in combination with a diluting agent which is non-miscible in water and which has a dielectric constant, measured at 20.degree. C., of less than 4.8 in order to form substantially water insoluble organophilic amine complexes which are extracted by the organic phase. The organic phase is thereafter decanted and separated from the aqueous phase, the amine complex is precipitated from the organic phase and the amine and non-miscible diluting agent are recovered from the organic phase and recycled for further use in the process. This process involves the use of a very substantial amount of the water insoluble amine as well as substantial amounts of organic solvent. Thus, as reported by the patent, the amount of amine employed should be at least 0.5% by volume which would be in excess of 5,000 ppm with respect to the total amount of water treated. The amount of organic solvent is at least 5% by volume with respect to the amount of water treated which would normally correspond to in excess of 50,000 ppm.
The foregoing amine-solvent extraction process has been investigated extensively and is reported to have a number of disadvantages including residual odors from the organic solvents and the tendency for emulsion formation during the treatment and regenerating steps of the process causing excessive loss of amine from the process in the formation of emulsions in the various intermediate steps of the process.